<h4>2.8 Resolutions related to reference systems</h4>
 
\subsection{IUGG 1991 Resolution}
\label{a-IUGG91}

{\bf Resolution No. 2}

The International Union of Geodesy and Geophysics 
  
considering the need to define a Conventional Terrestrial reference System (CTRS)
which would be unambiguous at the millimetre level at the Earth's surface and that
this level of accuracy must take account of relativity and of Earth deformation,
and

noting the resolutions on Reference Systems adopted by the XXIst General Asssembly
of the International Astronomical Union (IAU) at Buenos Aires, 1991,

endorses the Reference System as defined by the IAU at their XXIst General 
Asssembly at Buenos Aires, 1991, and

recommends the following definition of the CTRS:

{\em \bi
\item [1)] CTRS to be defined from a geocentric nonrotating system by a spatial
rotation leading to a quasi-Cartesian system,
\item[2)] the geocentric nonrotating system to be identical to the Geocentric
Reference System (GRS) as defined in the IAU resolutions,
\item[3)] the coordinate-time of the CTRS as well as the GRS to be the Geocentric
Coordinate Time (TCG),
\item[4)] the origin of the system to be geocentre of the Earth's mass including
oceans and atmosphere, and
\item[5)] the system to have no global residual rotation with respect to
horizontal motion at the Earth's surface.
\ei
}

\subsection{IAG 1991 Resolution}
\label{a-IAG91}

The International Association of Geodesy,

considering the IUGG Resolution on Conventional Terrestrial Reference
Systems (CTRS), and noting 
\bi
{\em
\item[1.] that the International Earth Rotation Service (IERS) is currently implementing such a system under the name
         of the International Terrestrial Reference System (ITRS) from VLBI, SLR, LLR and now GPS data, and 
\item[2.] that the ITRS is within one metre of WGS84, 
}
\ei
recommends: 
\bi
{\em
\item[1.] that groups making highly accurate geodetic, geodynamic or oceanographic analysis should either use the
         ITRS directly or carefully tie their own systems to it, 
\item[2.] that IERS standards should contain all necessary documentation to assist this task, 
\item[3.]that for mapping, navigation or digital databases where sub-metre accuracy is not required, WGS84 may be
         used in the place of ITRS, 
\item[4.]that for high accuracy in continental areas, a system moving with a rigid plate may be used to eliminate
         unnecessary velocities provided it coincides exactly with the ITRS at a specific epoch (e.g.,
         the ETRS 89 system
         selected by the EUREF subcommission)".   
}
\ei   
 
\subsection{IUGG 2003 Resolution establishing GGOS}
\label{a-iugg-ggos}

{\bf Resolution 3: Integrated Global Geodetic Observing System 
(IGGOS):} 

\noindent
IUGG Recognizing, 
\bi
{\em 
\item[1.] The great progress made in the use of
space and terrestrial techniques for monitoring the phenomena and
processes in the System Earth during the last decades; and 
\item[2.] The efforts made towards the integration of space
techniques in the management of observations, data processing,
evaluation, and modelling of the observable parameters, in particular
by the different international services; and
\item[3.] The urgent need to further develop and strengthen
the scientific and organizational collaboration of geodesy within the
geosciences; and
\item[4.] The necessity of generation and
accessibility of consistent products for users in Earth sciences,
neighbouring disciplines and society in general.
}
\ei
Considering, 
\bi
{\em
\item[ ]That the International Association of
Geodesy (IAG) has taken an initiative towards the realization of IUGG
Resolution no.1 adopted at the 22nd General Assembly in Birmingham 1999 
by installing the integrated Global Geodetic Observing System (IGGOS). \\
}
\ei
\bi
{\em
\item[]
Strongly supports the establishment of the IGGOS
Project within the new IAG structure as geodesy's contribution to the
wider field of geosciences and as the metrological basis for the Earth
observation programs within IUGG and the international organizations
mentioned in the 1999 Resolution no.1.
}
\ei
and Urges, 
\bi
{\em
\item[]That Associations cooperate with the new
project by providing data, models, products, and know-how useful for
IGGOS and the benefit of geosciences; and 
\item[]The participating in the IGGOS project by
joining the relevant components in its structure and assisting its
symposia and meetings.
}